1. Field of the Invention
This invention relates to a method for the continuous culture of yeast in which the vapor condensate from spent sulfite liquor is utilized as a carbon source. More particularly, the present invention relates to a method for producing yeast such as the Candida, Pichia or Hansenula species by an industrially acceptable procedure in a medium of a vapor condensate derived from the evaporation of spent sulfite liquor and which condensate contains added nutrients.
2. Description of the Prior Art
The principal carbon sources used for producing Torula yeast in existing commercial plants are mainly xylose which is present in spent sulfite liquor, saccharides, chiefly sucrose, which are used for the production of molasses yeast such as bakers yeast, and hydrocarbons, chiefly n-paraffins, for the production of petroleum yeast. Other carbon sources such as methanol and acetic acid have been studied for the culturing of yeast.
Because protein sources have become insufficient as a result of expanding human population, the production and supply of yeast as a protein source on an industrial scale is of increasing importance. A drawback to the commercial production of yeast is that the carbon sources described above have been a source of pollution which results from the residual carbon materials present in the waste medium. Because of the pollution problem, yeast production in Japan has recently declined. Thus, it seems that it will be impossible to continue to use spent sulfite liquor in the production of Torula yeast much longer, because it will be difficult to find appropriate counter-measures to meet the government's strict standards. It also appears that it will be impossible to continue the production of yeast in molasses media because of international fluctuations in price of molasses. In the case of petroleum media, the price of n-paraffins is also unstable and is increasing because of insufficient petroleum resources. These problems regarding the cost and availability of growth media makes it difficult to produce yeast less expensively. Other factors which raise the cost of waste liquor are the treatments necessary to reduce pollution.
Under these circumstances, alternative culture media such as methanol and acetic acid have been studied. These compounds have been successfully used on a laboratory scale, but have not been found to be useful industrially in the production of yeast because of the cost of the compounds.
A need therefore, continues to exist for a method of continuously culturing yeast at relatively low cost and for a method which involves fewer pollution problems.